
FISHES IN THEIR RELATION TO THE 
MOSQUITO PROBLEM > ^ ^ ^ 



From BULLETIN OF THE BUREAU OF FISHERIES, Volume XXVIII, 1908 
Proceedings of the Fourth International Fishery Congress : Washington, 1^08 




m'~y% WASHINGTON ::;;:: GOVERNMENT PRINTING OFFICE 



1910 



FISHES IN THEIR RELATION TO THE 
MOSQUITO PROBLEM ^ ^ ^ ^ 



From BULLETIN OF THK BUREAU OF FISHERIE.S, Volume XXVIH, 1908 



Pnnreduigs of the Fourth hitcrnational Fishery Co^tgrcss 



lVashi7igton , rgo8 




WASHINGTON :::;:: (",( >VI';RNMI';NT I'RINTING (.)1-FICK 



1910 



BUREAU OF FISHERIES DOCUMENT NO. 683 
Issued April, 1910 






.N^- 






FISHES IN THEIR RELATION TO THE MOSQUITO PROBLEM 

J- 
By William P. Seal 

J* 

Paper presented before the Fourth International Fishery Congress 
held at Washington, U. S. A., September 22 to 26. 1908 



831 



FISHES IN THEIR RELATION TO THE MOSQUITO PROBLEM. 



liy WII.I.IAM P. SKAI,. 
J* 

Some phases of the iiiosquito prublein are extremely simple and easy of 
solution, hut there are others that have not as yet attracted much attention 
and that, in the opinion of tlie writer, will not be so easily solved. The class 
of mosquitoes represented hy the rain-barrel wigglers constitutes, with the 
salt-marsh species, the most of the mosquitoes, and the most pestiferous of 
them as mere annoyances. The problem of dealint; with these is one of simple 
engineering, lilling and draining, with the oil barrel as an auxiliary. 

But the A)iopliclcs mosquito is altogether in another class and will require 
a very dilTerent and more complex sort of treatment. It is, in fact, to a great 
extent a separate problem. 

Though fewer in numbers than the other mosquitoes, the A)iopiliel(s is 
more to be dreaded because of its wary and insidious manner of attack and 
i>f its infectious ciiaracter. It tjrecds in Ijoth quiet and running water, but 
always where there is ample protection for its eggs and larva% among and over 
masses of aquatic or semiaquatic ])lants, confervse, duckweed, lily leaves, drift, 
lloating dead leaves, and debris. And, lying and moving horizontally on the 
water, so completelv does it assimilate witli its surroundings in both color and 
shape that it is only discernible to the sharpest vision, geiierally only by its 
movements, which are sidewise or l)ack\\ard on the surface unless seriously 
disturbed, when it wriggles down into the water. 

After a series of observations and experiments covering several years the 
writer is not convinced that Anopheles can be exterminated by any method so far 
advanced, or without very great dilliculty and the use of every available agency. 
The character and magnitude of the jiroblem are not yet understood. Several 
years ago, in an examination of Central Park, New York, Anopheles larvae were 
found to be abundant, though uj} to that time the locality was supposed to be 
free from them. They were found in unsuspected places, and not where the 
other mosquito larvae were found, and they were found al)undantly in other 
unsuspected places in New York as well. Moreover, although thousands of 

833 



834 BULLETIN OF THE BUREAU OF FISHERIES. 

dollars have since been spent in the attempt to destroy the breeding places, 
thcv are no doubt still occupied, within gunshot of the stately Fifth avenue 
homes and nearer to the iDcautiful playgrounds of the park. The same con- 
ditions will be found to prevail in every city. 

The most prolific source of Anopheles supply is the ornamental plant pond, 
which is becoming one of the most beautiful features of landscape gardening, 
public and private. These aquatic gardens provide A)wphelcs with habitats 
closely approximating the conditions it enjoys in nature, with, however, many 
protective advantages. Waters of this character can not be treated with oils 
or chemicals without destroying their beauty. Thus it becomes a serious 
problem how to destroy this pest and yet preserve the beauty of the ornamental 
plant pond. 

Anopheles, as well as all other mosquitoes, have numerous enemies in 
addition to fishes. All the aquatic beetles and their lar\'ge (and they are 
numerous), the dragon flies and their larvae, the Ijoat flies, the crane flies and 
their larva; (and where these latter are numerous few mosquito larvae will be 
found), the water skaters, and many others. 

The use of fishes for the purpose of destroying mosquito larvae is looked 
upon generally as an easy solution of the problem, and numbers of species have 
been recommended for the purpose, but so far as Anopheles is concerned the 
fishes have been generally useless. It is true that by their presence in the more 
open spaces they limit the areas in which mosciuitoes would otherwise propagate 
in great numbers, and no doubt they destroy some Anopheles, as well as some 
of all other species of mosquitoes. 

All small fishes, whether of the smaller species or the young of the larger 
kinds, will be found to eat mosquito larva- with avidity if supplied to them. 
This fact alone can not be taken as evidence of usefulness in this respect in a 
natural condition. Nevertheless, there is no doubt that the myriads of small 
fishes everywhere on the salt marshes and as well in all open waters, salt and 
fresh, prevent by their presence such a multiplication of moscjuitoes as would 
make life unendurable. In this respect even the most insignificant of the fishes 
are useful and merit our gratitufle. 

In considering the usefulness of fishes in this relation the natural habits 
and characteristics of a species are the only safe guides. That they will eat 
mosquito larva; if confined in an aquarium is to be expected. But will they 
do so in a natural condition? Will they seek for them as food? Stagnant 
water, where there is an abundance of plant life, affords such a great abundance 
and variety of larvae and other low forms of animal life that fishes could hardly 
be expected to develop epicurean tastes for particular kinds of larvae. They 
appear rather to gorge themselves with whatever comes in their way. The 



FISHES ANT) THE MOSQUITO PROBLEM. 833 

great need is lliat t litre- shall be enough mosquito eaters to consume all the 
other food that occurs and all the mosquitoes as well. And this means enormous 
numbers of fishes. What this involves is vet to be determined. We have no 
adecjuate conception of it. 

While, as has been stated, all fishes have some measure of usefulness, if 
only in the way of deterrent effect, there are only a few species likely to be found 
in waters in which mosquitoes breed, and especiallv where Auofyliclcs breeds. 
The most important of these are: The goldfish, which are introduced; several 
species of Fundithis (the killifishes) and allied genera; three or four species of 
sunfish; the roach or shiner; and one or two other small species of cvprinoids. 
In addition, there are a few sluggish and solitary species like the mud-minnow 
{Umbni) and the ])irate perch (Aphredodcrus) , which live among plants. The 
sticklebacks ha\e been mentioned in this connection, l)ut the Atlantic coast 
species are undoubtedly useless for the jiurjiose, being bottom feeders, living in 
the shallow tide pools and glitters, hidden among plants, or under logs and 
sticks at the bottom, uheri' they find an abundance of other food. 

In the salt marshes there are myriads of killitishes running in and out and 
over them with each tide, while countless numljers of other and smaller genera, 
such as Cypriiuhloii aiifl l.Kcauin, remain there at all stages of the tide. So 
numerous and active are all tlu'se that there is no possibility of the develop- 
ment of a mos(iuito wlu-re the>- have access. Of the killifishes two species, 
hctcroclilus and diaplunitts, ascend to the farthest reaches of tide How, but it is a 
question as to whether they would prove desirable for the purpose of stocking 
landlocked waters, since they are much like the English sparrow, aggressive 
toward the more peaceable and desirable kinds. Ivven t"r/>>/»oJo»;, which would 
seem to be a \aluable small species for the purpose, is viciously aggressive 
toward goldfish and no doubt all other cvprinoids. It is characteristic of all 
killifishes that they must be kejit by themselves in aquaria. They are the 
wolves and jackals of the smaller fishes. 

As a destroyer of Anopheles the writer has for several years advocated the 
use of Gambusia afjhiis, a small vivi])arous species of fish to be found on the 
south Atlantic coast from I )i'la\vare to I'lorida. A still smaller species of another 
genus, Jletcrandria jorniosa, ranging from 'j inch to ~s inch in length for 
the males to i inch or 1 ' s inches in length for the females, is generally to be 
found with Gambusia and is of the same general character. Both of these 
species are known as top minnows from their habit of being at the surface 
and feeding there; the conformation of the mouth, tlu- lower jaw projecting, 
is evidence of such feeding habit. P>oth are to be found in great numbers in 
the South in the shallow margins of lakes, ponds, and streams in the tide-water 
regions wherever there is marginal grass or aquatic or seniiaquatic vegetation to 



836 BULLETIN OF THE BUREAU OF FISHERIES. 

afford them shelter from the predaceous fishes. They are also to be found in 
shallow ditches and surface drains where the water is not foul, even where it is 
but the fraction of an inch deep. In fact, if any fishes will find their way to the 
remotest possible breeding places of the mosquito it will be Gambusia and 
Hcicrandria. And they are the only ones, so far as the writer's observation 
goes, that can lie considered at all useful as destroyers of Anopheles larvae. 

To what extent they could be acclimated in northern waters has yet to 
be determined. They are to be found in the Ohio Valley as far north as south- 
ern Illinois, hundreds of miles above tide water, where the climate must be 
quitevsevere. In 1905, at the earnest request of Prof. John B. Smith, state 
entomologist of New Jersey, the writer planted about 10,000 Gambusia and 
Heterandria in New Jersey waters. Some 8,000 were planted in one locality 
which was thought to afford very favorable conditions. In 1907 Mr. Henry 
W. Fowler, ichthvologist of the Academy of Sciences of Philadelphia, and 
author of " Fishes of New Jersey," found considerable numbers of Gambusia in 
the vicinity of Cape May, some 90 miles from where the plant was made. This 
opens up a verv interesting question. Mr. Fowler contends that Gambusia 
should be considered as indigenous to New Jersey. \^ery strong arguments 
to the contrary can he advanced, but the question is not of importance 
in connection with this paper, except that it either gives a farther northern 
range to the species or that, on the other hand, it shows the possibility of 
introducing them. 

The writer has come to the conclusion, after many experiments in small 
ponds, that a combination of the goldfish, which is ornamental and useful in 
the open water, the roach or shiner, which is a very active species, two small 
species of sunfish, which live among plants, and the top minnow would probably 
prove to be more effective in preventing mosquito breeding than any other 
fishes. The goldfish is somewhat lethargic in habit, and is also omnivorous, 
but there is no doubt that it will devour any mosquito larvse that may come 
in its way or that may attract its attention. The one great objection is that 
it grows too large and that it is cannibalistic, so that when a pond is once stocked 
with large goldfish the number of young to survive will be small. 

The roach is probably the most widely distributed and abundant of all 
the small fishes except the cyprinodonts. It is a very active fish, always ranging 
about in search of food. 

The two small species of sunfish, of the genus Enneacanthus, are very widely 
distributed. They live wholly among plants and feed upon larv-fe of all kinds. 

The top minnows are foragers always on the move in the search for food, 
skimming over the tops of plants with restless energv. 

All of the above-mentioned species are among the most abundant wherever 
found. If the range of the top minnows can be extended north it will prove to 



FISHES AND THE MOSQUITO PROBLEM. 837 

be a valuable aid. They are c[uite prolific, throwing off young to the number 
of perhaps lo to 20 at intervals of about a week from April to October. The 
young of May will be breeding l)y July or August the same year, thus giving 
a second generation in one summer. 

But notwithstanding all that has been said, it is a (juestion in the mind 
of the writer whether any combination of fishes will prove effective as against 
the Anopheles genus of mosquitoes imder present conditions of growing orna- 
mental aquatic plants. There must be a change in the construction and 
management of the water garden. As these are under the charge of intelligent 
men, it is only necessary that the problem should be understood and that 
the laws should compel the eradication of A>iopluics and provide for an espio- 
nage over the places where it breeds. But until some organized branch of 
the state governments takes up an investigation of this phase of the problem 
in a comprehensive manner nothing will be done. The magnitude of the task 
is not yet comprehended. It is quite possible that all of the beautiful masses 
of aquatics can be grown on mud alone without destroying their ornamental 
character, leaving the large open ones to the water in such a way that the fishes 
can do their work easily. In the great wild areas of swamp and stream aloof 
from human abodes the problem is more serious and will tax human ingenuity, 
but here only the hunter and fisherman are concerned. 

At present the attitude of the public mind toward suggested means of 
exterminating mosquitoes is good-naturedly tolerant but incredulous. And 
while the children are being crammed with Greek, Latin, and geometry they 
do not learn how to prevent the breeding of mosquitoes about their own homes 
or how properly to screen the houses in which they live. It is a lamentable 
fact that even where mosquitoes are most numerous and \irulent not one house 
in a hundred, it is safe to say, is mosquito-proof. There is an old saving that 
"What is everyljody's business is nobody's business." Practical work to be 
effective nuist lie somebody's particular business. Local boards of any kind 
can not easily rmi counter to individual sentiments and prejudices. It js the 
State alone that can overcome local stumbling blocks and inspire respect, and it is 
for this reason that attention is called to the seriousness of this problem and 
the suggestion offered that it is worthy of the serious consideration of those 
whose interest is in the waters where moscjuitoes breed and abound — the fish 
culturists and fishermen, represented by the fish and game commissions. 

In a paper prepared for the meeting of the American Mosquito Extermina- 
tion Society in 1905 the writer advanced the opinion that experimentation with 
and the supplying of fishes for the purpose of mosquito extermination is at least 
as properly the function of fish and game comn;issions as that of supplying 
them in the interests of sport and recreation, which is as much as can justly be 
claimed for trout culture. The mosciuilo problem in^•olves both the comfort 



838 BULLETIN OF THE BUREAU OF FISHERIES. 

and health of all classes of citizens. The desirability of the participation of 
fish commissions in the work, however, appears to the writer to be a question 
that can only be settled by submitting it to those who would be most nearly 
concerned with its practical operation, those engaged in fish-cultural work and 
who have at their command the necessary ecjuipment and knowledge. 

It may be argued that the study of the mosquito problem should devolve 
exclusively upon the agricultural departments. In 1900 or 1901 this question 
was suggested by the writer, and the Commissioner of Fisheries then decided 
that the work properly belonged to the entomological division of the Agricultural 
Department. At first thought this seems a logical conclusion; but when we 
come to realize fully the magnitude of the task one is compelled to conclude 
that its accomplishment will require the combined efforts of all the available 
resources of the States and probably of the National Government. 

The fish and game commissions have in their service a body of men whose 
duties include an espionage of both the land and waters of the States. By 
enlarging their powers and authority there is already available a capable organi- 
zation which needs only efficient direction and support to accomplish great 
practical results in this direction. 

There is another side to the question. The fish and game commissions 
do not have to the extent that they should the sympathy and support of the 
public in general, the prevailing idea being that they represent the interests 
of the sportsmen — gunners and anglers. And from this class alone there should 
be a vigorous support for such a development, not only because of the promise 
of greater comfort in their outings, but also because of the added popularity 
it would most surely give to the work of fish and game commissions and to 
legislation affecting the waters. If fish culture is to be progressive it must 
enlist the sympathy of all classes of citizens. It must justify itself by its use- 
fulness. Those engaged in it and in fish and game protection should welcome 
every opportunity to broaden the scope of fish work. There should be a desire 
to extend its popularity by enthusiastic support of any line of investigation 
or work which will benefit the public at large. There is now a precedent in 
the action of the United States Bureau of Fisheries in collecting and sending 
fishes to Hawaii for the purpose of mosquito destruction, and there is no reason 
why the fish and game commissions with their trained experts should not coop- 
erate in absolute harmony with the divisions of entomology, thus avoiding 
the creation of dual functions in state work. 



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